Answer:
They are similar by the definition of similarity in terms of a dilation.
Step-by-step explanation:
Given:
The vertices of ΔMNO are M (1, 3), N (4, 9), and O (7, 3). The vertices of ΔPQR are P (3, 0), Q (4, 2), and R (5, 0).
To choose: the correct option
Solution:
According to distance formula distance between points
is given by 
For ΔMNO,

For ΔPQR,

So,

Therefore, They are similar by the definition of similarity in terms of a dilation.
Two triangles are said to be similar if their sides are proportional.